| Cranberry is the most important fruit crop in Wisconsin, both in terms of acreage and economic value. Cranberry is a vegetatively propagated perennial plant that requires a large initial investment to prepare, plant, and nurture beds to full production. This makes the cost of diseases, especially viral diseases for which there are no treatments or cures, particularly high. In 2012, we discovered Tobacco streak virus (TSV) in cranberry plants bearing disfigured, scarred fruit, and TSV has since been detected in cranberry in New Jersey and Massachusetts. Plants which produced scarred, symptomatic TSV-positive fruit in one year produced non-scarred, asymptomatic TSV-positive fruit in subsequent years, consistent with the 'recovery' phenomenon previously documented in other ilarvirus-woody plant interactions. In field trials fruit set and berry weight were significantly reduced (p<0.05) in symptomatic, TSV-positive cranberry shoots but not in recovered, TSV-positive shoots compared to healthy, TSV-negative shoots. Likewise, return bloom in the first year following berry scarring was not negatively impacted in recovered shoots. Detection of TSV in various plant parts throughout the growing season was more variable in symptomatic shoots than in recovered shoots. Of all plant parts tested, TSV detection was lowest in berries at the time of harvest in both symptomatic and recovered shoots. In the field, incidence of TSV ranged from 1% to 71% across all beds and years tested. Minimal increases in incidence of TSV-infected shoots in cranberry beds from one year to the next, and spatial autocorrelation of TSV-infected shoots, suggest that most new infections result from TSV spreading within a bed, rather than frequent introductions of the virus from external sources. |
